1. Field of the Invention
This invention relates to a method and an apparatus for recording and reproducing a signal on and from an optical information recording medium such as an optical disc through the use of a laser beam. This invention particularly relates to a method and an apparatus for performing the trial writing and reading of test signals on and from a rewritable optical information recording medium such as a rewritable optical disc with a plurality of recording layers to decide optimum write-purpose powers of a laser beam applied to the recording medium. Preferably, the recording of user data on the recording medium is performed while the power of the laser beam is controlled at the decided optimum write-purpose levels. In addition, this invention relates to a rewritable optical information recording medium such as a rewritable optical disc with a plurality of recording layers. Furthermore, this invention relates to a computer program for recording and reproducing a signal on and from an optical information recording medium such as an optical disc through the use of a laser beam.
2. Description of the Related Art
There are DVDs (digital versatile discs) of various types such as a DVD-R (DVD-recordable) and a DVD-RW (DVD-rewritable). Some DVDs each have only a single recording layer while other DVDs each have multiple recording layers.
Regarding a typical single-layer DVD, optimum power control (OPC) is implemented as follows. To record a signal on the DVD, a recording laser beam modulated in accordance with the signal is applied to the DVD. The quality of the recorded signal on the DVD depends on the power of the laser beam applied thereto. The recording layer of the DVD has a power calibration area (PCA). Test recording and reproduction (trial write and read) are performed on the DVD before an information signal is recorded thereon. During the first half of the test recording and reproduction, test signals are sequentially recorded on the PCA in the DVD while the power of the laser beam is changed among different values. The test signals are assigned to the different powers of the laser beam, respectively. During the second half of the test recording and reproduction, the recorded test signals are reproduced, and the reproduced test signals are evaluated. An optimum power of the laser beam is decided on the basis of the results of the evaluation of the reproduced test signals. During the recording of an information signal on the DVD which follows the test recording and reproduction, the power of the laser beam is controlled at the decided optimum level.
Japanese patent application publication number 10-293926/1998 discloses a DVD-R which has a land track formed with pre-pits representing on-disc address information called LPP (land pre-pit) address information. Before the recording of information data on the DVD-R, the LPP address information is detected therefrom. During the recording of information data, the currently accessed position on the DVD-R is controlled according to the detected LPP address information.
Similarly, a DVD-RW has land pre-pits representing on-disc address information. It is known that the land pre-pits in the DVD-R or the DVD-RW represent not only the address information but also information about reference recording conditions such as a recommended recording laser power and a recommended recording laser waveform (a recommended recording strategy).
Japanese patent number 3259642 discloses a method and an apparatus for recording and reproducing a signal on and from a rewritable optical disc having a recording layer which can be changed between a crystalline state and an amorphous state depending on the power of a laser beam applied thereto. In Japanese patent 3259642, the power of the laser beam at which the recording layer changes from the crystalline state to the amorphous state to form a pit therein is referred to as the writing power (the recording power). The power of the laser beam at which the recording layer returns from the amorphous state to the crystalline state to erase a pit therefrom is referred to as the erasing power. During the recording of a new signal on the optical disc over an old recorded signal, the power of the laser beam is changed among the writing level, the erasing level, and a bottom level (a bias level). The bottom power is lower than the writing power and the erasing power. For the formation of every pit representing a portion of a newly recorded signal, the power of the laser beam is held at the erasing level for a certain interval to erase an old pit from the recording layer, and is then alternated between the writing level and the bottom level to form a new pit in the recording layer. In this case, the temporary laser power down to the bottom level prevents the unwanted diffusion of heat in the recording layer.
According to the method and the apparatus in Japanese patent 3259642, test signals are sequentially recorded on the optical disc while the writing power of the laser beam is changed among different values and the erasing power and the bottom power thereof remain fixed to certain values. The different values of the writing power are assigned to the recorded test signals, respectively. The recorded test signals are reproduced, and the reproduced test signals are evaluated through the use of characteristic parameters detected therefrom. The writing power value corresponding to optimum one among the detected characteristic parameters is decided to be optimum. One of the erasing power and the bottom power is referred to as the first power, and the other is called the second power. Thereafter, test signals are sequentially recorded on the optical disc while the writing power and the first power of the laser beam remain fixed to the optimum value and a certain value respectively and the second power thereof is changed among different values. The different values of the second power are assigned to the recorded test signals, respectively. The recorded test signals are reproduced, and the reproduced test signals are evaluated through the use of characteristic parameters detected therefrom. The second power value corresponding to optimum one among the detected characteristic parameters is decided to be optimum. Thereafter, test signals are sequentially recorded on the optical disc while the writing power and the second power of the laser beam remain fixed to the optimum values respectively and the first power thereof is changed among different values. The different values of the first power are assigned to the recorded test signals, respectively. The recorded test signals are reproduced, and the reproduced test signals are evaluated through the use of characteristic parameters detected therefrom. The second power value corresponding to optimum one among the detected characteristic parameters is decided to be optimum. As a result, the optimum writing power, the optimum erasing power, and the optimum bottom power of the laser beam are determined. During the recording of a new information signal on the optical disc over an old recorded information signal, the power of the laser beam is changed among the optimum writing level, the optimum erasing level, and the optimum bottom level. The characteristic parameters used for the evaluation of reproduced test signals are the asymmetry values, the modulation factors, the modulation-factor-derivative “γ” values, or the error rates of the reproduced signals.
In general, deciding the optimum recording power (the optimum writing power), the optimum erasing power, and the optimum bias power (the optimum bottom power) of a laser beam for a DVD-RW having multiple recording layers is more difficult than deciding those for a DVD-RW having only a single recording layer.